The phrase "solid residue" refers to the leftover solid material or substance that remains after a process or event, such as after burning something or after filtering a liquid. It is the solid material that remains behind. Full definition
Suitable substrates can be liquid slurries or wet solid residues. (cstwastewater.com)
Although new technologies have already been developed for the recovery of dissolved inorganic phosphates in the liquid fractions of municipal and agricultural wastes, solid residues remain a largely untapped source for phosphorus in its organic form. (sciencedaily.com)
The biproducts of fossil fuels are carbon monoxide, sulphites, nitrites, and solid residue which is non biodegradable. (answers.com)